Turned down for part time working

For a while now I've considered asking to work part time instead of full time as my OA is worsening. I have it in both big toes and my fingers. I think I'm also getting it in my left knee as I feel it clicking and it feels warm at times. I am having steroid injections in my feet now which do give some relief but my job involves interviewing people about public transport so I'm on my feet all day, sometimes on moving buses and trains. By the end of the working day my feet and sometimes my back hurts. I got to thinking that I have no real quality of life as I'm so tired and sore that I can do very little after work. On my days off I just catch up with housework.

So I asked to go part time. HR were very positive about it and asked my line manager to try to rush it through. Then the bombshell came. My line manager's boss has said no. His reason is that a colleague also wants to go to part time hours (also for health reasons). The boss said that if he agreed to both of us going part time then he would need to justify the need for a new full time employee to HR and he couldn't do that!

This sounds complete rubbish to me. My colleague has now gone on the sick and is considering handing his notice in. I am looking to change jobs but I enjoy my job, I just need to reduce my hours. A union rep sat in at the meeting with my boss and was pretty useless. My employer said that when my arthritis got bad they'd find me a bus station to work in where I can put my feet up! I'm going to look rude and ridiculous doing that. They said I can work in the office when I have flare ups. I don't drive and it takes an hour to commute there. However, the union guy thought this was reasonable.

I believe that he won't let me go part time because there are now only 3 of us left that are any good at my original job. 2 departments were amalgamated because of cutbacks. 6 of my original colleagues remained but 3 of them have since left because of the changes in the work. The remaining 2 work part time. My colleagues from the other department dislike our original work and find it difficult. However, management believe that because both types of work involve talking to the public, we should be able to cope with the changes. I am the only full time staff member that can successfully do both types of work and I think that's why he won't let me reduce my hours.

Is there anything I can do about this? Today I asked how much notice I have to give in the hope it would jolt them.